31 ビャクシン葉中の新奇C_<22>-テルペノイド炭化水素、JunipereneおよびIsojunipereneの構造、合成ならびに生合成仮説(ポスター発表の部)

抄録

A chromatographically unseparable mixture of two C_<22>-terpenoid hydrocarbons, juniperene (1) and isojuniperene (2), has been found to occur in the leaf wax of Juniperus chinensis L. cv. 'Kaizuka'. Their structures were determined by analyzing the mixture on the basis of NMR spectroscopy including 2D-INADEQUATE method and by degradating it into a racemic dicarboxylic acid 10. Furthermore, the syntheses of (-)-1 and (-)-2 from natural (-)-elemol demonstrated that the absolute stereostructures of juniperene and isojuniperene should be represented by (-)-1 and (+)-2, respectively. Although the proposed structures does not conform to the "isoprene rule", the compounds may be regarded as abnormal terpenoids which were biosynthesized by an enzymatic non-concerted [4+2]-cycloaddition reaction between pre-isogeijerene and β-myrcene and subsequent stereoselective Cope rearrangement, or by the stereospecific cycloaddition reaction between (±)-isogeijerene and β-myrcene, as shown in Fig. 5.